The briquetting machine produces the briquettes by successively supplying the materials between the pair of rotating rolls and applying the high-compressive force to the supplied materials (see Patent Documents 1 and 2, for example).
Conventionally, the briquetting machine for adjusting the briquette quality has been controlled by an operator to appropriately maintain the state of the briquetting machine, for example, the pressing load of the rolls, the power of the rolls, and the like. In this situation, as to the quality control in the production process of the briquettes by the briquetting machine, the operator regularly samples a part of the produced briquettes. The states of the sampled briquettes (briquette samples) can be determined as numeric values in consideration of the physical properties such as apparent density, crush strength, or the like. It is noted that the apparent density can be calculated by volume and weight of the briquette.